1. Technical Field
This invention relates to thin film metal alloy magnetic recording media for horizontal recording, and in particular to a cobalt alloy disk having high coercivity and low intrinsic media noise, and to a process for making such a disk.
2. Description of the Prior Art
One of the problems with thin film metal alloy magnetic recording media, such as cobalt alloy disks for horizontal recording, is that the intrinsic media noise increases with increasing linear recording density. Media noise arises from irregularities in the magnetic transitions and results in random shifts of the readback signal peaks. These random shifts are referred to as "peak jitter" or "time jitter". Thus, the higher the media noise, the higher the bit error rate. It is therefore desirable to develop a thin film metal alloy media which generates noise below a maximum acceptable level in order that data can be recorded at maximum linear density. The effect of intrinsic media noise, as measured by peak jitter and media signal-to-noise ratio (SNR), on the bit error rate in magnetic recording systems is described by Katz, et al., in "Effect of Bitshift Distribution on Error Rate in Magnetic Recording", IEEE Trans. on Magnetics, Vol. MAG-15, pp. 1050-1053, 1979. The measurement of media SNR is described by Belk, et al., in "Measurement of the Intrinsic Signal-to-Noise Ratio for High Performance Rigid Recording Media", J. Appl. Physics, 59(2), Jan. 15, 1986, pp. 557-562.
It has been proposed to improve the SNR of thin film cobalt alloy media by incorporating oxygen into the magnetic layer. For example, assignee's copending patent application 07/394,784, filed Aug. 16, 1989 describes a process for forming a low noise cobalt-platinum (CoPt) or cobalt-nickel (CoNi) alloy disk by sputtering the cobalt alloy in the presence of oxygen. Japanese Kokai 61-276116 describes a CoNi alloy disk with high SNR in which the CoNi magnetic layer is sputter deposited on an alumite-coated substrate in the presence of either oxygen or nitrogen, after which the disk is heat treated. While the oxygen doping of cobalt alloy magnetic layers improves the SNR, it also causes a significant reduction in coercivity. Thus it is desirable to be able to achieve both high coercivity and low intrinsic media noise in cobalt alloy media.